Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G12/00—Condensation polymers of aldehydes or ketones with only compounds containing hydrogen attached to nitrogen
  • C08G12/02—Condensation polymers of aldehydes or ketones with only compounds containing hydrogen attached to nitrogen of aldehydes
  • C08G12/04—Condensation polymers of aldehydes or ketones with only compounds containing hydrogen attached to nitrogen of aldehydes with acyclic or carbocyclic compounds
  • C08G12/10—Condensation polymers of aldehydes or ketones with only compounds containing hydrogen attached to nitrogen of aldehydes with acyclic or carbocyclic compounds with acyclic compounds having the moiety X=C(—N<)2 in which X is O, S or —N
  • C08G12/12—Ureas; Thioureas

Definitions

• urea-formaldehyde resins are normally manufactured in two stages. Urea and formaldehyde are mixed under neutral or slightly alkaline conditions at a mole ratio of formaldehyde to urea of 2:1 or more. The mixture is heated to almost reflux temperature to ensure that methylol ureas are formed. The solution thus obtained is then adjusted to a pH in the range of 6.5 to 5.0 and heated to reflux temperature (90°to 95° C.). The condensation is continued until the desired degree of condensation is achieved. The course of the polymerization can be watched by means of the following phenomena:
• the reaction is arrested by the addition of alkali until the sirup is slightly alkaline.
• Sufficient urea to give a final mole ratio of formaldehyde to urea of 1.5:1 or more is mixed into the syrup, either just before or after vacuum evaporation to remove water, or a part of the urea is added before and the remainder after vacuum evaporation to remove water.
• the product is then cooled to about 20° C. and is ready for use next day.
• the prior art resins which are normally manufactured in two stages have a rather high mole ratio of formaldehyde to urea (1.25 or more) and a rather high concentration of free formaldehyde.
• the process of the invention in which the urea is added in three or more portions in one continuous operation, yields urea-formaldehyde resins having a very low mole ratio of formaldehyde to urea (1.0:1.0 to 1.15:1.0) and an extremely low concentration of free formaldehyde.
• Such resins are suitable for use as binders in the manufacture of particle board and plywood type panels, which panels have a very low formaldehyde emission.
• the process of the invention eliminates the potential health hazard that is due to the use of conventional urea-formaldehyde resins, which use results in constant exposure of the workers to a high emission of free formaldehyde from the resin during the production of plywood and particle board in the factories, and in constant exposure of the end users to a high emission of free formaldehyde from the panels produced with the resins in homes, offices etc.
• the specific reaction conditions affect the structural character of the resin produced in terms of methylol groups, methylene linkages, methylene-ether linkages and molecular weight as well as molecular weight distribution.
• urea formaldehyde resins prior to cross-linking can be illustrated by the following formula: ##STR1## wherein R is hydrogen or a methylol group and n is the degree of polymerization. If R is hydrogen, an increase of the degree of polymerization will reduce the water miscibility of the resin and will prolong the hardening time of the resin. On the other hand, when R is a methlol group (--CH 2 OH), the colloidal stability and water miscibility of the resin will be improved markedly when the degree of polymerization is increased, and such resin will have a relatively short hardening time. A high degree of polymerization is required for good physical properties, such as strength, tackiness and adhesion.
• the present invention overcomes the drawbacks of the prior art.
• the process of the present invention produces urea-formaldehyde resins which have a low mole ratio of formaldehyde to urea and low concentrations of free formaldehyde together with good colloidal stability and relatively high rates of setting.
• the resins produced according to the invention have good adhesive properties for manufacturing particle board and plywood type panels.
• urea and formaldehyde are mixed in a mole ratio of urea to formaldehyde of about 1.0:2.0, and the mixture is heated to a temperature between 80° and 85° C. under alkaline conditions,
• the pH is then adjusted to a value in the range of 5.8 to 6.5, and the final mole ratio of urea to formaldehyde is adjusted to a value between 1.0:1.0 and 1.0:1.30, preferably in the range of 1:1.105 to 1:1.12, by adding urea, whereafter the condensate is cooled, and
• a known quantity of formalin is adjusted to a pH of 7.2 to 7.6 with a dilute sodium hydroxide solution, and mixed with urea in a mole ratio of formaldehyde to urea of 2.0:1.0.
• the solution thus obtained is heated to a temperature of 80° to 85° C.
• the pH of the reaction mixture is adjusted to a value in the range of 7.0 to 7.4, and the reaction is carried out for 20 to 40 minutes at the same temperature.
• the reaction mixture is then acidified to a pH of 4.8 to 5.8 with formic acid solution, while the temperature is still maintained at 80° to 85° C.
• the condensation reaction is continued at this temperature until the reaction mixture has a viscosity of 15 to 35 mPa.s as measured with a Brookfield Viscometer (spindle No. 1) at 65° C.
• the final mole ratio of total formaldehyde to total urea is adjusted to a value of 1.0:1.0 to 1.30:1.0 by the addition of urea. Heat is cut off, and the mixture is agitated for a further 20 to 30 minutes. The reaction mixture is cooled to around 60° C.
• the resin is evaporated in vacuo at 54° to 57° C. to about 66% solids and then cooled to below 40° C. At this temperature, the pH of the resin is finally adjusted to about 7.4. The product is best stored at a temperature around 20° C. It is ready for use the next day.
• the reactor used is fitted with an agitator.
• the reaction mixture is continuously agitated during the condensation.
• the resins produced by the process of the present invention are characterized by their very low mole ratio of formaldehyde to urea, which is lower than that of any of the stable resins known in the prior art. Resins with a mole ratio of formaldehyde to urea as low as 1.0:1.0 can be prepared. In spite of this extremely low mole ratio, the resins are still stable over a sufficient period of time, and their setting time is relatively short. The most important feature is that the resins produced by the process of the invention have free formaldehyde contents equal to or lower than 0.15%, which could not be attained in the prior art.
• the process of the invention is a major break through in the art of urea-formaldehyde resins, because the prior art resins with low mole ratios of formaldehyde to urea suffer from poor stability and poor reactivity.
• the chipboard and plywood panels produced by using the resins prepared by the process of the invention have good mechanical properties and water resistance.
• a reactor fitted with an agitator is used.
• the reaction mixture is agitated throughout the condensation.
• 2500 kg of 40% formalin are added to the reactor and neutralized with 40% sodium hydroxide solution to a pH of 7.4 under constant agitation.
• 1000 kg of urea are added, and the mixture is then heated to a temperature of 82° to 83° C. At this temperature, the pH is adjusted to 7.2.
• the condensation is carried out under these conditions for 30 minutes. Thereafter, the pH is adjusted to 5.4 with formic acid solution.
• the condensation is continued at the same temperature until the reaction mixture has a viscosity of 28 mPa.s as measured with a Brookfield Viscometer (spindle No. 1) at 65° C.
• a second quantity of 100 kg of urea is immediately added.
• the condensation is continued at the same temperature until the reaction mixture has a Brookfield viscosity (spindle No. 1) of about 68 mPa.s as measured at 65° C.
• the pH of the reaction mixture is then adjusted to 6.1 by the addition of 40% sodium hydroxide solution.
• a third quantity of 640 kg of urea is added, so that the final mole ratio of total formaldehyde to total urea is 1.15:1. Heat is cut off, and the final stage of the condensation is carried out for 25 minutes with agitation only. At the end of this time, the temperature of the reaction mixture has dropped to about 60° C.
• reaction mixture is evaporated under partial vacuum at 54° to 57° C. to 65.8% solids. It is then cooled to about 38° C., and the final pH is adjusted to 7.1 with 40% sodium hydroxide solution. The product is stored at about 20° C.
• a third quantity of 223 kg urea is added, while the reaction temperature of 85° C. is maintained. The condensation is continued until the reaction mixture has a Brookfield viscosity (spindle No. 1) of about 50 mPa.s as measured at 65° C. The pH is adjusted to 6.2 with 40% sodium hydroxide solution. The heat is then cut off.
• a fourth quantity of 467 kg of urea is added so that the final mole ratio of total formaldehyde to total urea is 1.10:1.
• the temperature is allowed to drop freely for 20 minutes.
• the reaction mixture is cooled to about 35° C., then the pH is adjusted to 7.2 with 40% sodium hydroxide solution.
• the final resin so obtained is cooled to 20° C. and stored at that temperature.
• the resin is suitable for plywood production as no dehydration has taken place.
• reaction mixture is agitated.
• the properties of the urea-formaldehyde resins obtained in Examples 1 and 2 are shown in Table I.
• the free formaldehyde content was determined by the sulfite method. It is lower than 0.15% in both resins.
• This Example compares the use of a low free formaldehyde resin prepared by the process of the invention in the production of particleboard with the use of a prior art urea-formaldehyde resin.
• the glue formulations used are as follows:

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Phenolic Resins Or Amino Resins (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)

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• 1983
  • 1983-12-09 GB GB08332962A patent/GB2150939B/en not_active Expired
• 1984
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  • 1984-11-27 CA CA000468663A patent/CA1242840A/en not_active Expired
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• 1985
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• 1987
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